My packrat-ness is getting to me, and I currently have 3 characters with banks just for storing items (one for purples, one for uniques, one for legendaries). What I'd really love to do is haxxor my Bank on one of those characters to be far larger. Gibbed's save editor seems to have potential but I don't see a specific option for this. I do however see a "raw" tab to edit specific data...but I also don't see any obvious way to do this.

So using Gibbed's save editor (or another tool) is there a way to modify my bank storage count for a character above the maximum you can otherwise buy via Eridium?

This looks like a very good answer (and first answer, too!) and presumably works. But can you elaborate a bit on what these values actually represent? I didn't understand whether it's adjusting the cost of the upgrades or unlocking them.
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MrLemonJan 19 at 9:26

I believe the values represent how many times an item has been upgraded through the Black Market. If you haven't done any Black Market upgrades, all the values would be 0 (hence, resetting the last two to 0 let's you buy all the Storage Upgrades again). If you have upgraded everything, all the values would be 7 except for the last two (which would be 9). Changing the Ammo values to 12, means they were upgraded beyond the default max of 7. The Ammo and Storage Deck upgrades operate differently, which is why you can't do the same thing to the Backpack and Bank as you can with the Ammo.
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bu11etpr00fJan 19 at 22:54

I know that the Value for the 8th line is for the Backpack, and the value for the 9th line is the Bank. The other values are for; Assault Rifle Ammo, Grenades, Pistol Ammo, Rocket Launcher Ammo, Shotgun Ammo, SMG Ammo, & Sniper Rifle Ammo, but I am not sure which is for which. That would take some testing. ;) I am pretty sure that 6 & 7 are for Grenades and Sniper Rifle Ammo though...just because I forgot to do them once, and they were the only ones not upgraded.
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bu11etpr00fJan 19 at 22:54

Upon further investigation, this might not actually be a permanent fix. Borderlands 2 appears to reset your Backpack back to 39 (or whatever) after quitting and restarting the game (unless you have more weapons than that, of course). I'll keep investigating to see what I can find. :)
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bu11etpr00fJan 19 at 23:37

The easiest, and only way that I know of is to use Gibbed to overstuff the bank with any bankable item, and then swap it out with what you want to keep (You must swap or you will lose the space). I think the max is 42 slots.

You can also do this with your backpack, but its more trouble than it is worth unless you never want to trade with others or purchase from machines. I tried adding slots via the raw tab multiple times but they never stay after removing an item from the bank. The slot was just gone. The game must overwrite the added slots unless there is something in them.

Hello and welcome to Arqade! We appreciate you answering but it seems like your answer is not easily readable and difficult to understand. Please format it and make paragraphs.
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Meraj99Mar 13 '13 at 10:24

Another thing you can do is retrieve the item code via Gibbed and save it to a text file (or word doc for example and accompany with screenshots or brief description). You can then reimport the item if you want/need it. It isn't often you need 42 different items in your current inventory so backing up the item codes is often enough.